Coupling CFD with 1D Model for the Prediction of Performance of a Hemodialysis Module with Undulated Fibers
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Hemodialysis is a medical treatment in which the function of the damaged kidneys of the patient is partially replaced by an artificial kidney, which consists in a hollow fiber membrane module [1]. Thanks to this module, toxins are selectively transferred from the blood, circulating inside the fibers (lumen-side) to the dialysate, circulating outside the fibers and in the external polymeric housing of the module (shell-side). One of the possible ways of enhancing the performances of a module that emerges from literature is the use of undulated fibers instead of straight fibers [2-3]. However, there is currently a gap in the literature regarding the quantification of enhanced mass transfer efficiency resulting from the alteration of hydrodynamic conditions within the module through fiber undulation. In this context, this work is aimed at developing a mathematical model which captures the hydrodynamic effect of the undulated fibers on the mass transfer efficiency (Sherwood number, Sh). The developed model is a multi-scale model: at fiber scale, it consists in a 3-D CFD model simulating the fiber and its surrounding fluid, the dialysate, and computes the flow field and the Sherwood number. At module scale, it includes a 1-D model simulating the whole dialyzer and calculates the solute clearance (clinical parameter indicating the efficiency of the hemodialysis treatment) using the Sherwood number obtained by 3-D simulations. The two models were implemented in Ansys CFX and Python, respectively, and then validated. According to the simulations’ results, the Sherwood number increases as the amplitude of the fiber increases and as the wavelength of the fiber decreases. However, the enhancement of Sh does not lead to an increase in clearance of the same magnitude.
